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Mattermost ServerApplication · Mattermost

CVE-2023-1777

MEDIUM · 5.3 CVSS v3.1 Published 2023-03-31
Fix available
A fix is available. Upgrade to 7.1.6 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Mattermost allows an attacker to request a preview of an existing message when creating a new message via the createPost API call, disclosing the contents of the linked message.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Mattermost's createPost API endpoint allows users to request previews of existing messages, but fails to properly validate authorization before returning the linked message contents. An attacker can exploit this by crafting API calls that reference arbitrary message IDs, bypassing access controls to read messages they shouldn't have permission to view.

MitigationImplement proper authorization checks in the createPost API to verify the requesting user has permission to access any linked message before returning its preview content.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Mattermost ServerApplication
Affected:< 7.1.6= 7.7.1= 7.8.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Mattermost Server version
    Access the Mattermost System Console > About page, or query the API endpoint /api/v4/system/config and look for the version field, or run 'mattermost version' from the server CLI
    Affected if The version is less than 7.1.6, or exactly 7.7.1, or exactly 7.8.0
  2. Verify createPost API endpoint is accessible
    Confirm the Mattermost server has the REST API enabled (default). The endpoint /api/v4/posts accepts POST requests for creating posts and can include message link previews
    Affected if The API is exposed and accepts requests from users who may not have full message access permissions
  3. Confirm message preview/linking feature is enabled
    Check the Mattermost config.json or System Console settings for 'Enable Message Attachments' or 'Allow Linking to Messages in Posts' - these features control whether previews of linked messages are generated
    Affected if Message linking or preview features are enabled, allowing the createPost API to fetch and display linked message contents

You are affected if you run an affected Mattermost Server version (less than 7.1.6, or 7.7.1, or 7.8.0) with the createPost API and message linking/preview features enabled, allowing unauthorized users to read restricted messages via crafted API calls.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 7.1.6 or later
Fixed in 7.1.6
Interim mitigation

Implement proper authorization checks in the createPost API to verify the requesting user has permission to access any linked message before returning its preview content.

Recommended fix Moderate confidence

Mattermost Server 7.8.1 or later (or latest stable 7.x release)

  1. 1. Identify the current Mattermost Server version by checking the System Console or running `mattermost version`
  2. 2. For versions < 7.1.6: Upgrade to Mattermost Server 7.1.6 or later (recommended: latest 7.x stable release)
  3. 3. For version 7.7.1: Upgrade to Mattermost Server 7.7.2 or later (recommended: latest 7.x stable release)
  4. 4. For version 7.8.0: Upgrade to Mattermost Server 7.8.1 or later (recommended: latest 7.x stable release)
  5. 5. After upgrade, verify the createPost API behavior to confirm the fix is applied
  6. 6. Review server logs for any signs of exploitation attempts prior to patching
Caveat Review Mattermost release notes for any breaking changes between your current version and the target version; major version upgrades may include schema changes requiring migration time

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,380
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-1777 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data